Using the brush border as the experimental system I propose to investigate the polarity of actin filaments relative to the plasma membrane. How calcium regulation occurs on the contractile apparatus of the brush border will also be studied. The control of actin polymerization in non-muscle cells will be investigated using the acrosomal reaction as the experimental system. Sperm will be lysed under conditions that stabilize the actin in the 'aggregated form.' The actin will then be dispersed with pH 8.0 and Mg ion. The supernatant containing G actin will be analysed for substances which inhibit polymerization. Limulus sperm will also be investigated to determine the nature of the 55,000 molecular weight protein and how it causes rearrangement of the actin to generate motion.